We experimentally investigate the effect of population viscosity (an increased probability to interact with others of one's type or group) on cooperation in a standard prisoner's dilemma environment. Subjects can repeatedly choose between two groups that differ in the defector gain in the...

We experimentally investigate the effect of imperfect separation of groups on group selection and cooperation in a standard prisoner¿s dilemma environment. Subjects can repeatedly choose between two groups, where in one of them an institutionalized norm fosters cooperation. The degree of...

We develop a simple model to study the coevolution of interaction structures and action choices in Prisoners' Dilemma games. Agents are boundedly rational and choose both actions and interaction partners via payoff-based imitation. The dynamics of imitation and exclusion yields polymorphic...

We experimentally explore the role of collective incentives in sustaining cooperation in finitely repeated public goods games with imperfect monitoring. In our experiment players only observe noisy signals about individual contributions, while total output is perfectly observed. We consider...